A team of researchers at MIT, however, believe they may have come up with a novel solution: wood. Using little more than a sapling branch from a sapwood pine and some plastic tubing, the researchers peeled the bark off the wood, inserted some plastic tubing, secured it using a clamp and epoxy, and then used it to filter water. First the team simply tried filtering red food dye, with a good rate of success. Then, as MIT News reports, they tried getting a little dirtier:

Finally, the team flowed inactivated, E. coli-contaminated water through the wood filter. When they examined the xylem under a fluorescent microscope, they saw that bacteria had accumulated around pit membranes in the first few millimeters of the wood. Counting the bacterial cells in the filtered water, the researchers found that the sapwood was able to filter out more than 99 percent of E. coli from water.

It's not all good news. While the sapwood filter appears able to handle most bacteria, viruses are much smaller and would most likely pass through the filter unhindered. The researchers are now looking into the potential of other plants to exhibit similar effects, with flowering trees being potentially able to filter even smaller particles thanks to their smaller pore size. The researchers are also trying to tackle the practical challenges of applying this technique in the field, including keeping the sapwood wet to retain its filtering capabilities.

The full research was published in the journal Plos One. Here's a very brief overview via GeoBeats News: